What event, involving two white dwarfs, can potentially restart core fusion and create a true star, albeit temporarily?

Answer

The merger of two white dwarfs

The merger of two white dwarfs can sometimes restart the furnace by pushing the combined mass past the critical point, potentially triggering runaway carbon fusion and a Type Ia supernova or forming a temporary, helium-fusing subdwarf.

What event, involving two white dwarfs, can potentially restart core fusion and create a true star, albeit temporarily?

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